Apparatus for stirring molten metal in container

ABSTRACT

An apparatus comprises a refractory-lined pipe (5) with a removable cover (6) formed with an opening provided to communicate the interior of the pipe (5) with a compressed gas supply system (8) and a vacuum system (9). This pipe (5) is arranged in a stepped conduit (4) of a tubular structure (3) from a refractory material. Positioned beneath the lower end of the pipe (5) and coaxially therewith on a stepped protection (10) of the wall of the conduit (4) formed in the structure (3) is a sleeve (11) from a porous material. Formed between the external side surface of the sleeve (11) and the wall of the conduit (4) is an annular space (12) confined from below by an annular cover (16) with an opening (17) for communicating the space (12) with a refining gas supply source (18).

TECHNICAL FIELD OF THE INVENTION

The present invention relates to metallurgy, and more particularly, toan apparatus for stirring molten metal in a container, e.g. directly inthe bath of a melting or holding furnace during its melting or vacuumdegassing. Such stirring is advantageously effected to enhance the rateof melting and vacuum degassing, as well as to maintain uniformity ofcomposition or temperature in a standing body of molten metal.

BACKGROUND ART

A variety of devices have been used for stirring molten metal directlyin the bath of a melting or holding furnace. This invention proposes adevice for gas dynamical stirring of molten metals, such as aluminum andits alloys, which is both effective in operation and simple inconstruction.

A device for stirring molten metal usually comprises a refractory-linedpipe with a removable cover, a system for feeding compressed air intothe pipe interior, and a system for building up vacuum therein.

This type of device is mounted in the wall of a melting unit through aport, disposed above the level of molten metal, in a manner to permitthe lower end of the pipe to be immersed in the melt. The deviceincorporates level gauges connected to the control circuit of thecompressed gas supply system and vacuum building-up system. This deviceis similar in operation to a pump or ejector which uses a pulse ofcompressed gas acting on the entire body of molten metal. The procedureof stirring a body of molten metal comprises the steps of alternatelywithdrawing molten metal upwardly from the body in a confined space to alevel above the body and expelling the withdrawn molten metal into thebody as a submerged high velocity jet. The alternate metal-withdrawingand metal-expelling steps are effected by alternately applying suctionand gaseous fluid (gas) under pressure in the confined space above thebody of molten metal. The jet of expelled metal creates turbulence inthe body of molten metal and thus effects its stirring.

The prior-art method makes it possible to enhance production efficiencyof a melting or holding furnace. In addition, the quality of metal beingstirred is improved by maintaining uniform chemical composition andtemperature throughout the melt bath. Jets of molten metal forcefullyexpelled from the ejector are poured over lumps of solid charge in afurnace to thereby enable their rapid melting.

On being tapped from a melting or holding furnace, the molten metal isfurther subjected to refining by means of gas, for example, argon.

However, gas-dynamic pumps used for stirring molten metal fail to ensureoptimum conditions for obtaining hihg-quality metal by way of reducingthe amount of gas, as well as slag and oxide inclusions containedtherein.

Attempts to effect refining of metal by applying a pulse of compressedgas thereto have ended so far in failure by reason of extremely shorttime of contact between gas and the surface of metal jet in the interiorof a stirrer pipe during metal-expelling procedure.

U.S. Pat. No. 3,895,937 discloses a method according to which a jet ofmolten metal discharged from a melting furnace into a vacuum holdingfurnace is rifined by means of gas. However, this method also fails toensure sufficiently high quality of metal due to a short time periodduring which refininf gas remains in contact with molten metal.

The known devices currently used for stirring and refining molten metalfail to meet ever growing demands for higher throughout capacity ofmelting furnaces and improved quality of metal. In other words, moresophisticated devices are needed today to satisfy increasing demands ofmodern industry.

Moreover, a demand has arisen for high-purity metals intended for themanufacture of vital units and parts to find wide application, forinstance, in the aircraft industry.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to obviate the abovedisadvantages.

The invention has as its aim the provision of an apparatus for stirringmolten metal in a container and of such construction that will permitsimultaneous stirring and refining of this metal.

This aim is attained in an apparatus for stirring molten metal in acontainer, comprising a refractory-lined pipe with a removable coverfitted with an opening provided to communicate the interior of the pipewith a compressed gas supply means and with a vacuum system, wherein thepipe is arranged in a stepped conduit of a tubular structure formed ofrefractory material, and wherein positioned below the lower end of thepipe and coaxially therewith on the stepped projection of the conduitwall is a sleeve made of a porous material, the external side surface ofsaid sleeve and the conduit wall forming an annular space confined frombelow by the projection and from above by an annular cover with anopening for communicating this space with the compressed gas supplymeans.

Such apparatus construction permits effective stirring of molten metal.Combining metal stirring and refining operations would permit enhancedproduction efficiency of melting units and improved quality of metal.Furthermore, melting units are rendered more reliable and easier inoperation; to additional equipment is required. Also, the stirrer pipeincorporated in such apparatus lends itself easily for replacement.

It is advantageous that the above-mentioned sleeve be formed of sponglytitanium.

This type of sleeve is simple in construction and permits easy passageof gas. It also has adequate heat-resisting properties and serves as agood catalyst during metal refining process.

It is preferable that a packing from a heat-resistant material, such askaolin or asbestos wool, be provided between the lower end of the pipeand the sleeve.

Such packing will assure reliable operation of the apparatus byabsorbing dynamic loads, and will facilitate the pipe removal.

The walls of the conduit of the tubular structure are preferably encasedin a metallic shell formed with an annular bottom and having its lowerend formed with a flange carrying the annular cover.

This will allow refining gas to be supplied through the sleeve made ofporous material, with the resultant increased efficiency of the refiningprocess. Moreover, such apparatus construction will facilitate assemblyand disassembly operations.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be further described, by way of example only, withreference to the accompanying drawing in which the sole FIGURE is avertical section showing an apparatus for stirring molten metal, and acontainer for the molten metal. The direction of metal and gas flows isindicated by arrows.

PREFERRED EMBODIMENT OF THE INVENTION

The illustrated apparatus for stirring a molten metal I in the bath of amelting furnace 2 (or holding furnace) comprises a tubular structure 3manufactured from a refractory material, such as refractory concrete.The tubular structure 3 is formed with a stepped conduit 4 accommodatinga refractory-lined pipe 5 with a removable cover 6. The tubularstructure 3 is mounted for easy replacement in the wall of the furnace 2(melting or holding). The interior of the pipe 5 communicates through anopening 7, provided in the wall or in the cover 6, with a compressed gassupply system 8 and with a vacuum system 9. The control circuit of thesesystems is not shown, as it is similar to that provided in anyconventional gas pump. Arranged underneath the lower end of the pipe 5and coaxially therewith on a stepped projection 10 of the wall of theconduit 4 is a sleeve II formed of a porous material, such as spongytitanium, which can serve as a catalyst in the process of refiningaluminum or its alloys. The pipe 5 and sleeve II are positioned in theconduit 4 of the tubular structure 3 with an annular space 12 formedtherebetween- At the place of disposition of the pipe 5, the wall of theconduit 4 of the tubular structure 3 is encased in a metallic shell 13formed with an annular bottom 14 adjoining the stepped projection 10 ofthe wall of the conduit 4. The upper end of the shell 13 is formed witha flange 15 having the pipe 5 fixed thereto with the aid of an annularcover 16. The annular cover 16 is fitted to confine the space 12 fromtop. The cover 16 is formed with an opening 17 provided to communicatethe space 12 with a source 18 of supplying refining gas. The refininfgas supply source 18 can be provided either as an independant system orelse can be connected to the compressed gas supply system 8 through apressure regulator (not shown). It is possible to maintain presettemperature conditions required for effective treatment of metal byheating or cooling gas in the gas supply system 8. Such temperaturecontrol system may be of any conventional design and therefore is notherein disclosed. The gas supply source 18 is brought in communicationthrough the opening 17 with the space 12 and further through the sleeveII with the interior of the pipe 5 for treating molten metal withrefining gas. The sleeve II is positioned below the minimum level ofmetal in the bath of the furnace 2 with the view to ensuring effectivestirring of metal. Placed between the sleeve II and the end of the pipe5 is a packing 19 formed of a heat-resistant resilient material, such askaolin or asbestos wool, which also facilitates the removal of the pipe5. The sleeve II may be stuck to the structure 3 by means of aheat-resistant composition. A maximum level 20 to which the metal I mayrise in the pipe 5 is shown with regard to those cases when theapparatus of the invention is adapted to application at the meltingfurnace 2.

The apparatus operates in the following manner.

At a minimum permissible level of the metal I in the furnace 2, when themetal covers the lower outlet opening of the pipe 5 and the sleeve II,the vacuum system 9 is brought in communication with the interior of thepipe 5, and refining gas is fed at a preset temperature and pressurefrom the source 18 into the space 12 and further through the sleeve IIinto the metal. Under the action of vacuum the molten metal I is raisedin the pipe 5 to reach the level 20. If the apparatus is employed at avacuum holding furnace, the level of the metal I will be the same in theinterior of the pipe 5 and in the furnace bath. Thereafter, the vacuumsystem 9 is cut off and the compressed gas supply system 8 is operatedto apply a pulse of compressed gas to the portion of metal treated withrefining gas, which is thereby expelled into the bath of the furnace 2.Then, another portion of the molten metal I is again sucked into theinterior of the pipe 5 to be treated with refining gas therein and to befurther expelled therefrom. Thus the metal stirring procedure iscombined with the metal refining process to continue until finishedmetal of a preset composition is obtained.

COMMERCIAL APPLICABILITY

The apparatus of the invention has been tested to show high operatingefficiency and to allow the amount of gas and other inclusions in themetal under treatment to be reduced from 15 to 20 percent, as comparedwith pumps of conventional construction.

The proposed apparatus is readily applicable to both holding and meltingfurnaces used to produce high-purity metals required for the manufactureof vital parts and units to meet the increasing demand of the aircraftindustry, machine-building industry and other related industries.

What is claimed is:
 1. An apparatus for stirring molten metal in acontainer, comprising a refractory-lined pipe with a removable coverfitted with an opening provided to communicate the interior of the pipewith a compressed gas supply means and with a vacuum system,characterized in that the pipe (5) is arranged in a stepped conduit (4)of a tubular structure (3) formed of refractory material, and whereinpositioned bellow the lower end of the pipe (5) and coaxially therewithon a stepped projection (10) of the wall of the conduit (4) formed inthe structure (3) is a sleeve (II) from a porous material, the externalside surface of said sleeve and the wall of the conduit (4) of thestructure (3) forming an annular space (12) confined from below by theprojection (10) and from above by an annular cover (16) with an opening(17) for communicating the annular space (12) with a refining gas supplysystem (18).
 2. An apparatus as claimed in claim 1, characterized inthat the sleeve (II) is formed of spongy titanium.
 3. An apparatus asclaimed in claim 1, characterized in that a packing (19) from aheat-resistant resilient material, such as kaolin or asbestos wool, isprovided between the lower end of the pipe (5) and the sleeve (II). 4.An apparatus as claimed in claim 1, characterized in that at the placeof disposition of the pipe (5) and the sleeve (II) the walls of theconduit (4) of the tubular structure (3) are encased by a metallic shell(13) formed with an annular bottom (14) and having its upper endprovided with a flange (15) carrying the annular cover (16) confiningthe annular space (12).